GPU & CPU setups, what is appropriate?
You can increase viewport speed in multiple ways.

1) Make sure you have GPU Compute on (in preferences and in render tab)
2) Adjust viewport resolution in Render Tab -> Performance -> Viewport -> Pixel size
3) Decrease Render samples in Render Tab -> Sampling -> Viewport
4) Remember that Cycles will always be considerably slower than Evee.  

Settings on my old machine:

Hope this helps.